The present invention relates to a mobile communication system using a cellular system.
In a mobile communication system, such as a mobile telephone system, the service area is divided into a plurality of small zones or cells, in each of which a base radio station is arranged. This arrangement is known as a cellular system. A cellular system effectively utilizes frequency resources by making it possible to use the same frequency band repeatedly between cells where no interference occurs.
A base radio station in a mobile telephone system primarily consists of an antenna, a duplexer, a transceiver for conversation and control purposes and a base station controller as described in FIG. 11.14, FIG. 11.16 and FIG. 11.17 Mobile Telephone (in Japanese) published by the Institute of Electronics, Information and Communication Engineers (edited under supervision by Moriji Kuwabara).
In a cellular system, the smaller the cell size, the more times the same frequency band can be used in repetition. Therefore, the cell size has to be reduced along with an increase of subscribers, and a microcellular system of about 200 m in cell radius is predicted to become required in the near future. In a microcellular system, it would be desirable to install base radio stations on existing street lamp poles and utility poles. However, since each base station of any existing type involves even a transceiver and a base station controller, it is too large to be mounted on a street lamp or utility pole.
Moreover, since the mobile terminals move around and perform communication in a mobile communication system, the traffic not only is geographically uneven but also varies from time to time. For instance, while the peak of traffic usually occurs in a downtown center in the daytime, it is dispersed into the suburbs at night. Furthermore if a traffic jam arises, the traffic around it might become significantly dense.
In order to provide adequate service quality, i.e. to ensure a low enough call blocking probability, against such a variable peak of traffic, the base station in each cell should be equipped with a sufficient number of speech transceivers to accommodate the heaviest predictable traffic in the cell. In such an arrangement, however, the utilization rate of each radio transceiver would approach 100% only in the peak period, but would be extremely low in other periods, resulting in a poor cost performance.